Table rows and CSS backgrounds - Test page

The following table has the first row with the headings styled with a background aligned to the right. The first heading cell in that row has a background aligned to the left.

By reasonable judging it would be obvious that the background applied tu the row woudl slide right under the background of the first cell.

But only Firefox renders it as such.

IE 6.0, 5.5, 5.0, Opera 8 render it a bit differently: the cells of the styled row inherit the background of their parent, resulting in the first cell having only its background, and the other ones having the background of the row aligned to the right of their own content box.

Opera 7.23 and 6.04 behave differently on their own: the first cell having only its background, the other cells having inherited the parent's background but having it miss-positioned.

Please give your thought on why is this happening?

TH 1 TH 2 TH 3
Lorem ipsum dolor sit amet, consectetuer adipiscing elit. Lorem ipsum dolor sit amet Lorem ipsum dolor sit amet
Lorem ipsum dolor sit amet, consectetuer adipiscing elit. Lorem ipsum dolor sit amet Lorem ipsum dolor sit amet